Apparatus and method for communication in broadcast system

ABSTRACT

The present disclosure relates to a communication apparatus and method for supporting a forward error correction scheme in a communication system. To this end, by means of a generation mode among a plurality of generation modes (ssbg_mode #0, #1, #2), a source symbol block having a plurality of source symbols is generated by using a source packet block having a plurality of source packets, and a repair symbol block for the generated source symbol block is generated by means of a forward error correction (FEC) scheme among a plurality of FEC schemes (FEC payload ID mode 0, FEC payload ID mode 1). A first FEC scheme (FEC payload ID mode 1) is applied to generate the repair symbol block, and in response to an occurrence of a discontinuity in packet sequence numbers, a repair packet may be generated to include length repair data and a repair FEC payload identifier (ID).

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a National Phase Entry of PCT InternationalApplication No. PCT/KR2019/000831, which was filed on Jan. 21, 2019 andclaims priority to Korean Patent Application No. 10-2018-0007401, whichwas filed on Jan. 19, 2018 and Korean Patent Application No.10-2018-0008962 filed on Jan. 24, 2018 in the Indian IntellectualProperty Office, the contents of which are incorporated herein byreference.

BACKGROUND 1. Field

The disclosure relates to a communication device and method supporting aforward error correction scheme in a communication system.

2. Description of the Related Art

Generally, broadcast systems use error correction schemes that supportreceiving devices to be able to repair missing data over the network.The forward error correction (FEC) scheme is a representative errorcorrection scheme that supports the receiving device to repair missingdata. The FEC scheme may be divided considering applied layers. Theapplication layer forward error correction (AL-FEC) scheme is an FECscheme in which FEC processing occurs in the application layer.

In the FEC scheme, e.g., the transmitting device may provide redundancyinformation for use to repair missing information to the receivingdevice. Here, the transmitting device and receiving device may generatethe redundancy information using an agreed-on algorithm. The algorithmmay generate the redundancy information using source information as aninput.

SUMMARY

In the FEC scheme-applied broadcast system, the transmitting device mayobtain repair symbols by performing FEC encoding on multiple sourcesymbols constituting the source symbol block. This should be preceded bychanging multiple source packets constituting the source packet blockinto multiple symbols constituting the source symbol block. The sourcepacket may be the MMT packet, e.g., when the moving picture expertsgroup (MPEG) media transport (hereinafter, “MMT”) protocol is used.

The source symbols may have the same length whereas the source packetsare variable in length. If the length of one source packet is largerthan the length of one source symbol, the one source packet may be splitinto a plurality of source symbols. Further, one source symbol maymaintain the same length using padding data.

Thus, for the receiving device to repair the missing source packet usingthe decoded source symbol block would need specifying the source symbolsconstituting the missing source packet and removing the padding data.

According to an embodiment of the disclosure, there is provided a methodand device of transmitting/receiving packets in a broadcast system.

Further, according to another embodiment of the disclosure, there isprovided a packet transmitting/receiving method and device that increasedata restoration efficiency in a broadcast system.

Further, according to still another embodiment of the disclosure, thereis provided a packet transmitting/receiving method and device that mayobtain efficient transmission reliability in a broadcast system.

Further, according to yet another embodiment of the disclosure, there isprovided a transmitting/receiving method and device, in which thereceiving device may specify the source symbols corresponding to thesource packet in the source block regardless of whether to receive thesource packet in a broadcast system.

Further, according to yet still another embodiment of the disclosure,there is provided a transmitting/receiving method and device that maylocate the start point of the missing source packet in the sourcesymbols of the repaired source symbol block in a broadcast system.

Further, according to yet still another embodiment of the disclosure,there is provided a transmitting/receiving method and device that mayremove padding data from the source symbols of the source symbol blockfully or partially repaired in a broadcast system.

Further, according to yet still another embodiment of the disclosure,there is provided a transmitting/receiving method and device that mayrepair all source packets with the source symbols of the source symbolblock fully or partially repaired in a broadcast system.

According to an embodiment of the disclosure, a method of generating atransmission packet by a transmitting device in a broadcast systemcomprises generating a source symbol block having plurality of sourcesymbols using a source packet block having a plurality of source packetsby one generation mode of a plurality of generation modes (ssbg_mode #0,#1, #2), generating a repair symbol block for the generated sourcesymbol block by one forward error correction (FEC) scheme of a pluralityof forward FEC schemes (FEC payload ID mode 0, FEC payload ID mode 1),generating a source packet by the plurality of source packets, andgenerating a repair packet by the generated repair symbol block.

Here, generating the repair packet includes generating the repair packetin which length repair data and a repair FEC payload identifier (ID) areincluded in response to an occurrence of a discontinuity of a packetsequence number, and a first FEC scheme (FEC payload ID mode 1) beingapplied to generate the repair symbol block.

According to an embodiment of the disclosure, a transmitting device of abroadcast system comprises a transmitter configured to transmit atransmission packet to an external device for a broadcast service and aprocessor connected with the transmitter and configured to generate thetransmission packet for the broadcast service.

Here, the at least one processor is configured to generate a sourcesymbol block having plurality of source symbols using a source packetblock having a plurality of source packets by one generation mode of aplurality of generation modes (ssbg_mode #0, #1, #2), generate a repairsymbol block for the generated source symbol block by one forward errorcorrection (FEC) scheme of a plurality of forward FEC schemes (FECpayload ID mode 0, FEC payload ID mode 1), generate a source packet bythe plurality of source packets, and generate the repair packet in whichlength repair data and a repair FEC payload identifier (ID) are includedin response to an occurrence of a discontinuity of a packet sequencenumber, and a first FEC scheme (FEC payload ID mode 1) being applied togenerate the repair symbol block.

According to an embodiment of the disclosure, a method of restoring atransmission packet by a receiving device in a broadcast systemcomprises receiving a source packet including a plurality of sourcepackets and a repair packet including a repair symbol block, identifyingwhether a packet sequence number is disconnected and a fist FEC scheme(FEC payload ID mode 1) among a plurality of FEC schemes (FEC payload IDmode 0, FEC payload ID mode 1) is applied, to generate the repair symbolblock based on a plurality of flags included in a repair forward errorcorrection (FEC) payload identifier (ID) of the repair packet, decodinglength repair data of the repair packet in response to an occurrence ofthe packet sequence number and the first FEC scheme (FEC payload IDmode 1) being applied, and restoring a missing transmission packet usingthe decoded length repair data.

Here, the plurality of flags include a first flag (D: discontinuityflag) indicating that the discontinuity of the packet sequence numberhas occurred, a second flag (I) indicating whether the length repairdata is included in the repair packet, a third flag (F:FEC_parameter_flag) indicating whether the same FEC code is used togenerate the repair symbol block and the length repair data, and afourth flag (N: num_LRS_flag) indicating whether the number of repairsymbols included in the length repair data is the same as the number ofrepair symbols included in the repair packet, and wherein the repair FECpayload identifier (ID) further includes information about a lengthconfigured considering the first to fourth flags.

According to an embodiment of the disclosure, a receiving device of abroadcast system comprises a receiver configured to receive a sourcepacket including a plurality of source packets and a repair packetincluding a repair symbol block and a processor connected with thereceiver and configured to repair a source packet received through thereceiver.

Here, the at least one processor is configured to identify whether apacket sequence number is disconnected and a fist FEC scheme (FECpayload ID mode 1) among a plurality of FEC schemes (FEC payload ID mode0, FEC payload ID mode 1) is applied, to generate the repair symbolblock based on a plurality of flags included in a repair forward errorcorrection (FEC) payload identifier (ID) of the repair packet, decodelength repair data of the repair packet in response to an occurrence ofthe packet sequence number and the first FEC scheme (FEC payload IDmode 1) being applied, and repair a missing transmission packet usingthe decoded length repair data.

Here, the plurality of flags include a first flag (D: discontinuityflag) indicating that the discontinuity of the packet sequence numberhas occurred, a second flag (I) indicating whether the length repairdata is included in the repair packet, a third flag (F:FEC_parameter_flag) indicating whether the same FEC code is used togenerate the repair symbol block and the length repair data, and afourth flag (N: num_LRS_flag) indicating whether the number of repairsymbols included in the length repair data is the same as the number ofrepair symbols included in the repair packet, and wherein

Here, the repair FEC payload identifier (ID) further includesinformation about a length configured considering the first to fourthflags.

BRIEF DESCRIPTION OF DRAWINGS

Particular preferred embodiments of the present disclosure and theforegoing and other aspects, features, and advantages will be apparentfrom the following detailed description taken in conjunction with theaccompanying drawings, wherein:

FIG. 1 is a view illustrating a hierarchical structure of an electronicdevice supporting a broadcast service to which various embodimentsproposed in the disclosure are to be applied;

FIG. 2 is a view illustrating a two-stage FEC encoding structure towhich various embodiments proposed in the disclosure are to be applied;

FIG. 3 is a view illustrating a scheme of generating a source symbolblock in an LA-FEC encoding structure having two layers to which variousembodiments proposed in the disclosure are to be applied;

FIG. 4 is a view illustrating an example encoding symbol block in abroadcast system according to an embodiment of the disclosure;

FIG. 5 is a view illustrating a source symbol block generated usingssbg_mode 0 in a broadcast system according to an embodiment of thedisclosure;

FIG. 6 is a view illustrating an example source symbol block generatedusing ssbg_mode 1 in a broadcast system according to an embodiment ofthe disclosure;

FIG. 7 is a view illustrating an example source symbol block generatedusing ssbg_mode 2 in a broadcast system according to an embodiment ofthe disclosure;

FIG. 8 is a view illustrating an example FEC source packet format in abroadcast system according to an embodiment of the disclosure;

FIG. 9 is a view illustrating an example FEC repair packet format in abroadcast system according to an embodiment of the disclosure;

FIG. 10 is a view illustrating an example source FEC payload ID in abroadcast system according to an embodiment of the disclosure;

FIG. 11 is a view illustrating an example SS_ID configuration methodwhen an LA_FEC encoding scheme is used in a broadcast system accordingto an embodiment of the disclosure;

FIG. 12 is a view illustrating an example repair FEC payload ID in abroadcast system according to an embodiment of the disclosure;

FIG. 13 is a view illustrating an example of generating a source symbolblock in a source packet block using ssbg_mode 2 in a communicationsystem according to an embodiment of the disclosure;

FIG. 14 is a view illustrating another example FEC repair packet formatin a broadcast system according to an embodiment of the disclosure;

FIG. 15 is a view illustrating an example repair FEC payload ID in abroadcast system according to an embodiment of the disclosure;

FIG. 16 is a view illustrating a source symbol block generated usingssbg_mode 2 in a broadcast system according to an embodiment of thedisclosure;

FIG. 17 is a view illustrating an example length symbol block for packetlength information protection in a broadcast system according to anembodiment of the disclosure;

FIG. 18 is a view illustrating an example encoding symbol block when apacket drop is applied in a broadcast system according to an embodimentof the disclosure;

FIG. 19 is a view illustrating an example length encoding symbol blockwhen a packet drop is applied in a broadcast system according to anembodiment of the disclosure;

FIG. 20 is a view illustrating an operation procedure of a transmittingdevice in a broadcast system according to an embodiment of thedisclosure;

FIG. 21 is a view illustrating an operation procedure of a receivingdevice in a broadcast system according to an embodiment of thedisclosure;

FIG. 22 is a view schematically illustrating an internal structure of atransmitting device in a broadcast system according to an embodiment ofthe disclosure; and

FIG. 23 is a view schematically illustrating an internal structure of areceiving device in a broadcast system according to an embodiment of thedisclosure.

It should be noted that the same or similar reference denotations may beused to refer to the same or similar elements, features, or structuresthroughout the drawings.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure are described withreference to the accompanying drawings. However, it should beappreciated that the present disclosure is not limited to theembodiments, and all changes and/or equivalents or replacements theretoalso belong to the scope of the present disclosure. The same or similarreference denotations may be used to refer to the same or similarelements throughout the specification and the drawings.

As used herein, the terms “have,” “may have,” “include,” or “mayinclude” a feature (e.g., a number, function, operation, or a componentsuch as a part) indicate the existence of the feature and do not excludethe existence of other features.

As used herein, the terms “A or B,” “at least one of A and/or B,” or“one or more of A and/or B” may include all possible combinations of Aand B. For example, “A or B,” “at least one of A and B,” “at least oneof A or B” may indicate all of (1) including at least one A, (2)including at least one B, or (3) including at least one A and at leastone B.

As used herein, the terms “first” and “second” may modify variouscomponents regardless of importance and do not limit the components.These terms are only used to distinguish one component from another. Forexample, a first user device and a second user device may indicatedifferent user devices from each other regardless of the order orimportance of the devices. For example, a first component may be denoteda second component, and vice versa without departing from the scope ofthe present disclosure.

It will be understood that when an element (e.g., a first element) isreferred to as being (operatively or communicatively) “coupled with/to,”or “connected with/to” another element (e.g., a second element), it canbe coupled or connected with/to the other element directly or via athird element. In contrast, it will be understood that when an element(e.g., a first element) is referred to as being “directly coupledwith/to” or “directly connected with/to” another element (e.g., a secondelement), no other element (e.g., a third element) intervenes betweenthe element and the other element.

As used herein, the terms “configured (or set) to” may beinterchangeably used with the terms “suitable for,” “having the capacityto,” “designed to,” “adapted to,” “made to,” or “capable of” dependingon circumstances. The term “configured (or set) to” does not essentiallymean “specifically designed in hardware to.” Rather, the term“configured to” may mean that a device can perform an operation togetherwith another device or parts. For example, the term “processorconfigured (or set) to perform A, B, and C” may mean a generic-purposeprocessor (e.g., a CPU or application processor) that may perform theoperations by executing one or more software programs stored in a memorydevice or a dedicated processor (e.g., an embedded processor) forperforming the operations.

The terms as used herein are provided merely to describe someembodiments thereof, but not to limit the scope of other embodiments ofthe present disclosure. It is to be understood that the singular forms“a,” “an,” and “the” include plural references unless the contextclearly dictates otherwise. All terms including technical and scientificterms used herein have the same meaning as commonly understood by one ofordinary skill in the art to which the embodiments of the presentdisclosure belong. It will be further understood that terms, such asthose defined in commonly used dictionaries, should be interpreted ashaving a meaning that is consistent with their meaning in the context ofthe relevant art and will not be interpreted in an idealized or overlyformal sense unless expressly so defined herein. In some cases, theterms defined herein may be interpreted to exclude embodiments of thepresent disclosure.

Hereinafter, various embodiments of the present invention are describedin detail with reference to the accompanying drawings.

FIG. 1 is a view illustrating a hierarchical structure of an electronicdevice supporting a broadcast service to which various embodimentsproposed in the disclosure are to be applied.

Referring to FIG. 1, an electronic device may have a structure in which,e.g., the AL-FEC applies to the MMT. That is, the electronic device mayhave a layered structure including an MMT application layer, a protocollayer, a transport layer, and an internet protocol (IP) layer. Theelectronic device may be a transmitting device or receiving devicesupporting, e.g., broadcast services.

The transmitting device determines assets needing protection in the MMTpackage and the number of FEC source flows to protect the assets. OneFEC source flow may protect one or more assets. The FEC source flow maybe configured of MMTP packets transferring one or more assets. The FECsource flow and its configuration information may be transferred in anFEC scheme.

The FEC scheme may generate repair symbols constituting one or more FECrepair flows using one or more FEC codes. The repair symbols may betransferred, along with the FEC payload ID, to a receiving device basedon the MMT protocol. That is, the transmitting device may transfer FECsource packets and FEC repair packets to the receiving device using theMMT protocol.

The MMT protocol of the receiving device may transfer the FEC sourceflow and one or more FEC repair flows related to the FEC source flow inan FEC scheme. An FEC method may attempt to repair missing MMTP packetsand transfer the repaired MMTP packets via the MMT protocol.

The FEC scheme proposes a scheme that splits the FEC source flow intosource packet blocks and generates source symbol blocks with the sourcepacket blocks. The generated source symbol blocks are FEC-encoded by theFEC code. Here, FEC encoding means generating the repair symbol blockconstituted of repair symbols using the source symbol block constitutedof source symbols. An FEC encoding algorithm may be used to create therepair symbol block in the source symbol block. As an example, the FECencoding algorithm specified in ISO/IEC 23008-10 may be used.

The FEC scheme may be operated in one mode of two different modes, i.e.,FEC payload ID mode 0 and FEC payload ID mode 1. FEC payload ID mode 0adds the source FEC payload ID to the MMTP packet, and FEC payload IDmode 1 makes no change to the existing MMTP packet.

The FEC scheme may configure packets including layered or non-layeredmedia data with multiple levels using the FEC encoding structure. Thisenables applying a necessary degree of protection level to each assetconstituting one FEC source flow. The FEC source flow may be the MMTPsub flow transferring a signaling message. The FEC encoding structuremay include, e.g., a two-stage FEC encoding structure and a layer-awareFEC (LA-FEC) encoding structure.

FIG. 2 is a view illustrating a two-stage FEC encoding structure towhich various embodiments proposed in the disclosure are to be applied.

Referring to FIG. 2, one source packet block 210 may be split into M(>1) source packet blocks 220-1, 220-2, . . . , 220-M. The split-intosource packet blocks 220-1, 220-2, . . . , 220-M may be converted into Msource symbol blocks 230-1, 230-2, . . . , 230-M by one of a pluralityof source symbol block generation schemes (ssbg modes or source symbolblock generation modes). The M source symbol blocks 230-1, 230-2, . . ., 230-M each are encoded using the first FEC code 240.

A single source symbol block 230 may be generated by connecting the Msource symbol blocks 230-1, 230-2, . . . , 230-M, and the generatedsingle source symbol block 230 may be encoded using a second FEC code250.

By encoding each of the M source symbol blocks 230-1, 230-2, . . . ,230-M using the first FEC code 240, M repair symbol blocks (1^(st)_P1,2^(nd)_P1 . . . M^(th)_P1) are generated. One repair symbol block P2 isgenerated by encoding the single source symbol block 230 using thesecond FEC code 250.

The LA-FEC encoding structure is an FEC encoding structure specified formedia data (e.g., SVC, MVC, etc.). The LA-FEC encoding structure usesinter-media layer association and each media layer has associated FECrepair flows. Here, the FEC repair flow protects the data of theassociated media layers and all media layers (which are hereinafterreferred to as complementary layers) on which the associated medialayers rely.

In the LA-FEC encoding structure, the source packets including the dataof each media layer are grouped into different source symbol blocks perlayer. The source symbol blocks used to generate the repair symbolsconstituting one FEC repair flow are in the form of a combination of asource symbol block constituted of data of the media layer associatedwith the FEC repair flow and source symbol blocks constituted of thecomplementary layer data of the associated media layer. The combinationof the source symbol blocks constituted of the data of different layersfollows the hierarchical structure of media. That is, each source symbolblock may follow the source symbol block constituted of thecomplementary layer data of the media data contained in the sourcesymbol block.

The source symbol block and repair symbol block generated as describedabove, may form one encoding symbol block, and the repair symbol blockP2 generated from the single source symbol block 230 may be combinedwith the one encoding symbol block.

FIG. 3 is a view illustrating a scheme of generating a source symbolblock in an LA-FEC encoding structure having two layers to which variousembodiments proposed in the disclosure are to be applied.

In FIG. 3, enhancement layer (Enh. Layer) refers to a layer relying onthe base layer in the hierarchical media stream.

FIG. 4 is a view illustrating an example encoding symbol block in abroadcast system according to an embodiment of the disclosure.

Referring to FIG. 4, the encoding symbol block is configured of thesource symbol block and the repair symbol block generated by the sourcesymbol block. The source symbol block may be configured according to thescheme agreed on by the transmitting device and the receiving device.

The broadcast system may define, e.g., one or more source symbol blockgeneration schemes and, as necessary, select one of them and generatethe source symbol block. Hereinafter, source symbol block generationscheme is denoted an SSBG mode. The SSBG mode selected by thetransmitting device may be transferred to the receiving device via asignaling message.

According to an embodiment, the encoding symbol block consists of asource symbol block including K source symbols and a repair symbol blockincluding repair symbols. It should be noted that the source symbols andrepair symbols belonging to the encoding symbol block have the samelength, T bytes.

In the broadcast system supporting multimedia services, the FEC sourceflow is split into source packet blocks and protected. The sourcepackets belonging to the source packet block may have a constant orvariable length. The source packet block may be converted into thesource symbol block according to the SSBG mode, for FEC encoding.

The broadcast system supporting multimedia services may use three kindsof SSBBG modes, named, e.g., ssbg_mode0, ssbg_mode1, and ssbg_mode2.ssbg_mode0 may be used only when all of the MMT packets constituting onesource packet block have the same length. ssbg_mode1 and ssbg_mode2 maybe used even when the MMT packets constituting one source packet blockhave different lengths.

Embodiments where FEC payload ID mode 0 is applied are described belowwith reference to FIGS. 5 to 12, and embodiments where FEC payload IDmode 1 is applied are described with reference to FIGS. 13 to 17.

FIG. 5 is a view illustrating an example source symbol block generatedusing ssbg_mode 0 in a broadcast system according to an embodiment ofthe disclosure.

Referring to FIG. 5, when ssbg_mode 0 is used, all the MMT packetsconstituting one or more (M) source packet blocks may have the samelength. In this case, the number (K) of the source symbols constitutingthe source symbol block is identical to the number (K) of the sourcepackets, i.e., MMT packets, constituting the source packet block. Forexample, this denotes that the ith MMT packet of the source packet blockis the same as the ith symbol of the source symbol block (i=0, 1, . . ., K−1). When the two-stage FEC encoding structure or LA-FEC encodingstructure is applied (M>1), the ith source symbol block is generatedfrom the ith source packet block (i=0, 1, . . . M−1).

FIG. 6 is a view illustrating an example source symbol block generatedusing ssbg_mode 1 in a broadcast system according to an embodiment ofthe disclosure.

Referring to FIG. 6, when ssbg_mode 1 is used, each of the sourcesymbols constituting the source symbol block may, as necessary, have apadding byte, so that its length becomes identical to the length of theMMT packet associated with the source symbol. Except for this, thesource symbol block may be generated in the same manner as ssbg_mode 0.That is, the number (K) of the MMT packets included in one source packetblock is identical to the number (K) of the source symbols included inone source symbol block associated with the source packet block.

According to ssbg_mode 1, the ith source symbol of the source symbolblock may start with two octets arranged in order of network byte(higher octet first) indicating the length of the ith MMT packet of thesource packet block associated with the ith source symbol of the sourcesymbol block. Then, the octets of MMT packet # i are arranged, and therest is filled with 0 octets.

When the two-stage and LA_FEC encoding structure (M>1) is used, the ithsource symbol block may be generated from the ith source packet block(i=0, 1, . . . M−1), and the source symbols belonging to each sourcesymbol block may include the padding byte (00h) at the end.

FIG. 7 is a view illustrating an example source symbol block generatedusing ssbg_mode 2 in a broadcast system according to an embodiment ofthe disclosure.

Referring to FIG. 7, the five MMT packets constituting one source packetblock are individually 34, 30, 56, 40, and 48, and the five MMT packetsmay be arranged in the eight source symbols constituting one sourcesymbol block. At this time, the size T of source symbol is 32, and eachsource symbol may consist of two symbol elements (T′=T/2=16 bytes).

According to an embodiment, in ssbg_mode 2, one source symbol block maybe generated from the source packet block including Ksp source packets.The one source symbol block may include Kss source symbols. All sourcesymbols each may include N symbol elements. This means that one sourcesymbol block consists of N*Kss symbol elements.

MMT packet #0 of the source packet block may be positioned at first s0symbol elements of the associated source symbol block.

More specifically, the first two bytes of the first symbol element amongthe s0 symbol elements may start with the two octets in order of networkbyte indicating the length of MMTP packet #0. The subsequent may befilled with octets of MMTP packet #0, and the rest with zero octets. Thefirst MMT packet of the source packet block, along with the 0th MMTpacket, may be arranged at the next s1 symbol elements in the sourcesymbol block. After filling is done up to # Ksp−1 in the same manner, ifKss*T−sum {si*T/N, i=0 . . . Ksp−1} is not 0, zero octets are arrangedin the remaining symbol elements of the source symbol block.

In the two-stage and LA-FEC encoding structure, a single source symbolblock for the second FEC code is generated by connecting all the sourcesymbol blocks generated from M source packet blocks.

Definitions of specific values in SSBG mode

Ksp: number of MMT packets (source packets) in source packet block

Kss: number of source symbols in source symbol block

Ri: octet of ith MMT packet to be added to source symbol block

Si: length of Ri represented in unit of octet

Li: Si value denoted with two octets in order of network byte

T: source symbol size represented in bytes

N: number of symbol elements constituting one source symbol

T′: size (T′=T/N) of symbol element represented in bytes

si: smallest integer meeting si*T/N=siT′>=(Si+2)

Pi: si*T′−(Si+2) zero octets

P: Kss*T−sum {si*T′, i=0 . . . Ksp−1} zero octets

At this time, the source symbol block may be configured by sequentiallyconnecting Li, Ri, and Pi(i=0 . . . Ksp−1) and P and then splitting theresult into source symbols with a size of T.

MMT packet, which is one transmission packet in the broadcast systemsupporting multimedia services, may be divided into FEC source packetand FEC repair packet. The FEC source packet has a format fortransmitting the source packet, and the FEC repair packet has a formatfor transmitting the repair symbol.

FIG. 8 is a view illustrating an example FEC source packet format in abroadcast system according to an embodiment of the disclosure.

Referring to FIG. 8, an FEC source packet may have a format in which asource FEC payload ID is added to an MMTP packet including an MMTPpacket header, an MMTP payload header, and an MMTP payload. The sourceFEC payload ID may provide information for identifying the source symbolor symbol element carried by the FEC source packet.

FIG. 9 is a view illustrating an example FEC repair packet format in abroadcast system according to an embodiment of the disclosure.

Referring to FIG. 9, an FEC repair packet may have a format of includingan MMTP packet header, a repair FEC payload ID, and one or more repairsymbols. The repair FEC payload ID may provide information foridentifying the repair symbol(s) and related source packet blockincluded in the FEC repair packet.

When ssbg_mode 0 or ssbg_mode 1 is used, the FEC repair packet shouldinclude only one repair symbol. When ssbg_mode 2 is used, the FEC repairpacket may include one or more repair symbols.

Among the FEC repair packets belonging to the FEC repair packet block,the one or more other FEC repair packets than the last FEC repair packetshould include the same number of repair symbols.

According to an embodiment, the transmitting device using the MMT FECscheme should transfer, to the receiving device, information(hereinafter, ‘FEC configuration information’) needed to repair thesource packet lost in the receiving device. The FEC configurationinformation may include the source FEC payload ID. The FEC configurationinformation may be included and transmitted in the FEC source packetand/or FEC repair packet according to its usage and characteristics. TheFEC configuration information may also be transmitted via a separatepacket for a signaling message which is neither the FEC source packetnor FEC repair packet.

FIG. 10 is a view illustrating an example source FEC payload ID in abroadcast system according to an embodiment of the disclosure.

In FIG. 10, an example of usage of the SS_ID field and FFSRP_TS field isas follows.

SS_ID (32 bits)—denotes a sequence number for identifying the sourcesymbols included in the relevant FEC source packet. After the maximumvalue, the sequence number goes back to 0.

When ssbg_mode 0 or ssbg_mode 1 is used, the SS_ID value is increased byone per FEC source packet. When ssbg_mode==10, the sequence number isincreased by one per symbol element (including the symbol elementsconstituted only of padding), and the SS_ID value is set to the sequencenumber of the first symbol element included in the FEC source packet.

When the LA-FEC encoding structure is used, the lowest SS_ID of thesource symbol block should be identical to SS_ID_max+1. Here, SS_ID_maxis the highest SS_ID of the leading source symbol block of all theflows.

FIG. 11 is a view illustrating an example SS_ID configuration methodwhen an LA_FEC encoding scheme is used in a broadcast system accordingto an embodiment of the disclosure.

Referring to FIG. 11, the first SS_ID of the same source symbol block ineach flow may be used as a synchronization point of all the sourcesymbol blocks of all the flows.

FFSRP_TS(4 bytes)−FFSRP_TS consists of TS_Indicator(1 bit) and FP_TS(31bits).

TS_Indicator(1 bit)—denotes the time stamp in FEC (refer to Table 1).For the one-stage FEC encoding structure and LA-FEC, the value of thisfield should be set to “0.”

In the case of two-stage FEC encoding structure (M>1), if it is set to“1,” this denotes that FP_TS (31 bits) is a value for the FEC source orrepair packet block.

If set to “0,” this denotes that the next FP_TS (31 bits) is a value forthe ith FEC source or repair packet block (M>1 and i=1, 2, . . . M) ofthe two-stage FEC encoding structure.

In the case of the two-stage FEC encoding structure (M>1), for theodd-numbered FEC source packets of the ith FEC source packet block, thisfield is set to “0” and, for the even-numbered FEC source packets of theith FEC source packet block, the field should be set “1.” (i=1,2, . . ., M).

Table 1 below describes the TS_Indicator value.

TABLE 1 value description b0 The next FP-TS (31 bits) is for the FECsource or repair packet block of the one-stage FEC and LA-FEC encodingstructure or the ith FEC source or repair packet block of the two-stageFEC encoding structure (M > 1 and i = 1, 2, . . . , M) b1 The next FP_TS(31 bits) is for the FEC source or repair packet block of the two-stageFEC encoding structure.

FP_TS (31 bits)—FP_TS denotes the other 31 bits than the MSB in the32-bit time stamp present in the packet header of the first MMTP packettransmitted in the relevant FEC source packet block/FEC repair packetblock.

According to an embodiment, FFSRP_TS may selectively exist. Thesignaling message transferred via separate packets except for the FECsource/repair packet may include a flag indicating whether there is,e.g., FFSRP_TS.

The repair FEC payload ID of the FEC configuration information may bepresent after the MMTP packet header in the FEC repair packet as in theexample of the FEC repair packet format shown in FIG. 9.

FIG. 12 is a view illustrating an example repair FEC payload ID in abroadcast system according to an embodiment of the disclosure.

In FIG. 12, each field may be defined as follows.

SS_Start(32 bits)—denotes the border of the associated source symbolblock. When ssbg_mode 0 or ssbg_mode 1 is used, it is set to thesequence number of the first source symbol of the associated sourcesymbol block. When ssbg_mode 2 is used, it is set to the sequence numberof the first symbol element of the associated source symbol block.

RSB_length(24 bits)—is the number of all the repair symbols of therepair symbol block including one or more repair symbols transmitted viathe corresponding FEC repair packet.

RS_ID(24 bits)—is a sequence number for identifying the first repairsymbol included in the corresponding FEC repair packet. When the FECrepair packet includes two or more repair symbols, the sequence numberof one or more subsequent repair symbols to the first repair symbol isincreased by one. This is why the sequence number is assigned as itstarts with 9 and increases by 1 for the repair symbols included in eachrepair symbol block.

SSB_length[N](N*24 bits)—when the LA-FEC encoding structure is not used,N is “1,” and SSB_length denotes the number of source symbols includedin the associated source symbol block (when ssbg_mode 0 or ssbg_mode 1is used) or the number of source symbol elements included in theassociated source symbol block (when ssbg_mode 2 is used, the sourcesymbol elements all of which are constituted of padding are excluded).

When the LA-FEC encoding structure is used, N should be identical tonumber of complementary layers+1, and SSB_length[i] denotes the numberof source symbols included in the associated source symbol block of theith flow (when ssbg_mode 0 or ssbg_mode 1 is used) or the number ofsymbol elements included in the associated source symbol block of theith flow (when ssbg_mode 2 is used, the source symbol elements all ofwhich are constituted of padding are excluded).

FFSRP_TS(4 bytes)—consists of TS_Indicator(1 bit) and its subsequentFP_TS(31 bits).

TS_Indicator(1 bit)—denotes the time stamp in FEC (refer to Table 2).For the one-stage FEC encoding structure and LA-FEC, the value of thisfield should be set to “0.” In the case of the two-stage FEC encodingstructure (M>1), the value of the field indicates the usage of FP_TS (31bits). That is, if the value of the field is set to “1,” this denotesthat FP_TS (31 bits) is a value for the FEC source or repair packetblock. If the value of the field is set to “0,” this denotes that thenext FP_TS (31 bits) is a value for the ith FEC source or repair packetblock (M>1 and i=1, 2, . . . M) of the two-stage FEC encoding structure.

In the case of the two-stage FEC encoding structure (M>1), for theodd-numbered FEC source packets of the ith FEC source packet block, thisfield is set to “0” and, for the even-numbered FEC source packets of theith FEC source packet block, the field may be set “1.” (i=1, 2, . . . ,M).

Table 2 below defines the TS_Indicator value.

TABLE 2 value description b0 The following FP-TS (31 bits) is for theFEC source or repair packet block of the one-stage FEC and LA-FECencoding structure or the ith FEC source or repair packet block of thetwo-stage FEC encoding structure (M > 1 and i = 1, 2, . . . , M) b1 Thefollowing FP_TS (31 bits) is for the FEC source or repair packet blockof the two-stage FEC encoding structure.

FP_TS (31 bits)—denotes the other 31 bits than the MSB in the 32-bittime stamp present in the packet header of the first MMTP packettransmitted in the relevant FEC source packet block/relevant FEC repairpacket block.

The AL-FEC message carries the configuration information of AL-FECscheme to the receiver or network entity.

Table 3 to Table 5 show an example AL-FEC message format.

TABLE 3 No. of Syntax Values bits Mnemonic AL FEC ( ){  message_id 16 version 8  length 16  message_payload{ fec_flag 1 bslbfprivate_fec_flag 1 bslbf reserved “111111” 6 bslbf if (fec_flag==1) { length_of_fec_flow_descriptor 16 uimsbf  fec_flow_descriptor( ) {number_of_fec_flows N1 8 uimbsf for ( i=0; i<N1 ; i++) {  fec_flow_id 8uimbsf  source_flow_id 8 uimbsf  number_of_assets N2 8 uimbsf  for (j=0; j<N2 ;j++) { packet_id 16 uimbsf  }  fec_coding_structure 4 uimbsf ssbg_mode 2 uimbsf  ffsrpts_flag 1 bslbf  fec_payload_id_mode 1 bslbf length_of_repair_symbol 16 uimbsf  if (ssbg_mode == 10) {num_of_repair_symbol_per_packet 16 uimbsf 16 uimbsf  }  if(fec_coding_structure == 0001) { repair_flow_id 16 uimbsffec_code_id_for_repair_flow 8 uimbsf if (private_fec_flag == 1) { private_flag 1 bslbf  private_field_length N3 7 bslbf  private_fieldN3*8 uimbsf }

TABLE 4 maximum_k_for_repair_flow 24 uimbsf maximum_p_for_repair_flow 24uimbsf protection_window_time 32 uimbsf protection_window_size 32 uimbsf} if (fec_coding_structure == 0010) { num_of_sub_block_per_source_block8 uimbsf number_of_parity_flows N4 8 uimbsf for ( k=0; k<N4 ;k++){repair_flow_id 16 uimbsf fec_code_id_for_repair_flow 8 uimbsf if(private_fec_flag == 1) { private_flag 1 bslbf private_field_length N5 7bslbf private_field N5*8 uimbsf } maximum_k_for_repair_flow 24 uimbsfmaximum_p_for_repair_flow 24 uimbsf protection_window_time 32 uimbsfprotection_window_size 32 uimbsf } }

TABLE 5  if (fec_coding_structure == 0011) { num_of_layer_for_LAFEC N6 8uimbsf fec_code_id_for_repair_flow 8 uimbsf if (private_fec_flag == 1) { private_flag 1 bslbf  private_field_length N7 7 bslbf  private_fieldN7*8 uimbsf } for ( l=0;l<N6 ;l++){  repair_flow_id 16 uimbsf maximum_k_for_repair_flow 24 uimbsf  maximum_p_for_repair_flow 24uimbsf  protection_window_time 32 uimbsf  protection_window_size 32uimbsf }  } }  } }  } }

Table 3 to Table 5 describe the usage of each of the fields constitutingthe AL-FEC message.

message_id—an identifier for identifying the AL-FEC message.

version—version information for AL-FEC message.

length—the 16-bit field indicating the byte length of the AL-FECmessage. Denotes the length from the next field to the last byte of theAL-FEC message, wherein 0 is not allowed.

fec_flag—denotes whether at least one source flow protected by AL-FECexists. When none of the source flows are AL-FEC protected, thefollowing message is not transferred.

Table 6 defines the value of the fec_flag field.

TABLE 6 value description 0 There is no FEC source flow 1 There is atleast one FEC source flow.

private_fec_flag—denotes the presence of private FEC information. Whenthe value is “0,” this denotes that any FEC code identified with thesubsequent fec_code_id_for_repair_flow field does not need private FECinformation. When the value is “1,” this denotes that the presence orabsence of private FEC information and its length are provided using, atleast, one byte (private_flag and private_field_length) for all the FECcodes identified with the subsequent fec_code_id_for_repair_flow field.

length_of_fec_flow_descriptor—byte length of fec_flow_descriptor

number_of_fec_flows—number of FEC-encoded packet flows (FEC encodedflows)

fec_flow_id—an integer for identifying the FEC-encoded packet flow. EachFEC-encoded packet flow has one associated FEC source flow and one ormore FEC repair flows.

source_flow_id—an integer for identifying the FEC source flow. Each FECsource flow has one associated FEC-encoded packet flow.

number_of_assets—number of assets included in the corresponding FECsource flow.

packet_id—packet_id field value of MMTP packet header.

ssbg_mode—SSBG mode value.

Table 7 defines valid values of ssbg_mode field.

TABLE 7 value Meaning b00 ssbg_mode0 (with constant MMTP packet size)b01 ssbg_mode1 (with variable MMTP packet size) b10 ssbg_mode2 (withvariable MMTP packet size) b11 Reserved

ffsrpts_flag—denotes whether FFSRP_TS(32 bits) exists in all source FECpayload IDs and repair FEC payload IDs.

Table 8 defines valid values of ffsrpts_flag field.

TABLE 8 value description b0 None of source FEC payload IDs and repairFEC payload IDs include FFSRP_TS (32 bits). b1 All source FEC payloadIDs and repair FEC payload IDs include FFSRP_TS (32 bits).

fec_payload_id_mode—FEC payload ID mode as applied.

Table 9 defines valid values of fec_payload_id_mode field.

TABLE 9 value description b0 FEC payload ID mode 0 b1 FEC payload IDmode 1

length_of_repair_symbol—byte length of repair symbol.

Number of repair symbols transmitted with one FEC repair packet whennum_of_repair_symbol_per_packet—ssbg_mode 2 is used.

Number of symbol elements constituting one source symbol whennum_of_symbol_element_per_source_symbol—ssbg_mode 2 is used.

fec_coding_structure—FEC encoding structure applied to associated FECsource flow.

Table 10 defines allowed values of fec_coding_structure field.

TABLE 10 value description b0000 AL-FEC does not apply b0001 One-stageFEC encoding structure b0010 Two-stage FEC encoding structure b0011Layer-aware FEC encoding structure b0100 to b1111 Reserved

num_of_sub_block_per_source_block—number of split-into source packetblocks constituting one source packet block in two-stage encodingstructure.

number_of_repair_flows—number of FEC repair flows.

num_of_layer_for_LAFEC—number of layers of media protected inlayer-aware FEC encoding structure.

repair_flow_id—integer for identifying repair FEC flow. Denotes thepacket_id value of the MMTP packet header of the FEC repair packet. Thepacket_id value of the FEC repair flow is repair_flow_id.

fec_code_id_for_repair_flow—identifier of FEC code applied to associatedFEC repair flow.

private_flag—when this is set to “1,” it denotes that there exists aprivate field for transferring private FEC information for a specificFEC algorithm. When it is set to “0,” this denotes that there is noprivate field.

Table 11 defines allowed values of private_flag field.

TABLE 11 value description b0 There is no private field for specific FECalgorithm b1 There is private field for specific FEC algorithm

private_field_length—byte length of private field. Whenprivate_flag=“0,” the value should beset to “0” to indicate that thereis no private_field.

private_field—includes private FEC information for a specific FECalgorithm.

maximum_k_for_repair_flow—maximum allowed number of source symbolsconstituting one source symbol block.

maximum_p_for_repair_flow—maximum allowed number of repair symbolsconstituting one repair symbol block.

FEC protection window means the number of packets or time when all ofthe packets belonging to the related FEC source packet block/FEC repairpacket block should be transmitted. Thus, the difference between thetime stamp of the last packet transmitted among the packets belonging tothe related source packet block/repair packet block and the time stampof the first packet transmitted should not exceed the FEC protectionwindow.

protection_window_time—denotes the maximum time difference between thefirst packet display among the packets belonging to the related FECsource packet block/FEC repair packet block and the last packettransmitted in unit of 1/1000 second (millisecond). When the value ofthis field is “0,” “protection_window_size” is used.

protection_window_size—denotes the maximum packet count between thefirst packet display among the packets belonging to the related FECsource packet block/FEC repair packet block and the last packettransmitted. When the value of this field is “0,”“protection_window_time” is used.

As described above, the FEC scheme may be operated in two differentmodes. The two modes may be FEC payload ID mode 0 and FEC payload IDmode 1. FEC payload ID mode 0 adds the source FEC payload ID to the MMTPpacket, and FEC payload ID mode 1 is a mode that makes no change to theMMTP packet.

The encoding symbol of FEC payload ID mode 1 is the same as that in FECpayload ID mode 0. That is, the source packets (MMT packets) belongingto the source packet block are arranged in the same order as packet_idprovided for the FEC-encoded packet flow of the AL-FEC message. When thesame packet_id applies, they are arranged in ascending order ofpacket_sequence_number.

The source symbol block of FEC payload ID mode 1 is the same as thesource symbol block when ssbg_mode 0 and ssbg_mode 1 are used.

FIG. 13 is a view illustrating an example of generating a source symbolblock in a source packet block using ssbg_mode 2 in a communicationsystem according to an embodiment of the disclosure.

Referring to FIG. 13, it is assumed that one source packet blockconsists of, e.g., five MMTP packets, and the five MMTP packets areindividually 34, 30, 56, 40, and 48. The five MMTP packets may bearranged in the source symbol block constituted of eight source symbols.The size T of each of the eight source symbols would be 32. Each of theeight source symbols may consist of two symbol elements (T′=T/2=16bytes).

According to the above assumption, one MMTP packet may be disposed atone or multiple source symbols. For example, MMTP packet #0 having asize of 34 bytes would first be arranged at two symbol elementsconstituting one source symbol (SS #0) having a size of 32 bytes. Theremaining two bytes in MMTP packet #0 are arranged at the first symbolelement of the two symbol elements constituting the next source symbol(SS #1). The remaining two bytes of MMTP packet #0 are arranged at thefirst symbol element, and the remaining bytes may be filled with paddingdata. The remaining four MMTP packets may be arranged at the remainingsource symbols using the same rule.

In FEC payload ID mode 1, the FEC source packet lacks source FEC payloadID and thus has the same format as the existing MMTP packet.

FIG. 14 is a view illustrating another example FEC repair packet formatin a broadcast system according to an embodiment of the disclosure.

Referring to FIG. 14, an FEC repair packet may include an MMTP packetheader, a repair FEC payload ID, length repair data, and one or morerepair symbols. The length repair data may be selectively present, andits presence or absence may be known through the repair FEC payload ID.The length repair data is information for protecting the length symbolconstituted of two octets, and each length symbol denotes the length ofeach packet belonging to the associated source packet block and thelength of dropped packet.

Further, when ssbg_mode 0 or ssbg_mode 1 is used, the FEC repair packetshould include only one repair symbol. When ssbg_mode 2 is used, the FECrepair packet may include one or more repair symbols.

Further, among the FEC repair packets belonging to the FEC repair packetblock, all the other FEC repair packets than the last FEC repair packetshould include the same number of repair symbols.

FIG. 15 is a view illustrating an example repair FEC payload ID in abroadcast system according to an embodiment of the disclosure.

Referring to FIG. 15, among the fields included in the repair FECpayload ID, the field providing information per asset (packet_id),SS_start_seq_nr[i], L[i], and SPB_length[i] follow the order ofpacket_id provided via the AL-FEC message. Further, this order is thesame as the order in which the source symbols are arranged in the sourcesymbol block.

An example of usage of each field shown in FIG. 15 is as follows.

Discontinuity_flag(D, 1 bits)—denotes that there is discontinuity in thepacket_sequence_number field present in the MMTP packet header of theFEC source packet generated by the source packets having the samepacket_id included in the source packet block protected by the FECrepair packet.

When the corresponding value is set to, e.g., “0,” there should be nodiscontinuity in the packet_sequence_number field values of the sourcepackets having the same packet_id included in the source packet block.

When the value is, e.g., “1,” the value of the I field presentthereafter should be set to “1.”

T(1 bit)—denotes whether the timestamp field exists. When the value is,e.g., “0,” no timestamp field exists and, when the value is, e.g., “1,”a timestamp field exists.

SSM(2 bits)—denotes the length of SS_start_seq_nr[i] fields presentthereafter. The length of the SS_start_seq_nr[i] field is “8+8*SSM bit”.

I(1 bit)—denotes the presence or absence of length repair data. When thevalue is set to, e.g., “1,” the length repair data should exist and,when the value is set to, e.g., “0,” the length repair data should notexist. When the value of the D field is “1” or SSBG Mode 2 is used, thevalue should be set to “1.”

FEC_parameter_flag(F, 1 bits)—denotes whether the length repair data hasbeen generated using the same parameter and the same FEC code as therepair symbol of FEC repair packet. When the value is, e.g., “0,” L3,LRSB_length, L6, LSB_length field do not exist. When the value is, e.g.,“1,” L3, LRSB_length, L6, LSB_length field exists. The field should beset to “0” when the value of I field is “0” and, when the value of the Dfield is “1,” it should be set to “1.”.

num_LRS_flag(N, 1 bits)—denotes whether the number of length repairsymbols included in the length repair data of the current FEC repairpacket is the same as the number of repair symbols included in thecurrent FEC repair packet.

When the value is set to, e.g., “0,” the length repair data shouldinclude the same number of repair symbols as the number of repairsymbols included in the current FEC repair packet, and there should notbe L5, LRS_ID, L7 and num_LRS fields.

When the value is set to, e.g., “1,” the length repair data may includea different number of repair symbols from the number of repair symbolsincluded in the current FEC repair packet, and there should be L5,LRS_ID, L7 and num_LRS fields.

The field should be set to “0” when the value of I field is “0” and,when the value of the F field is “1,” it should be set to “1.”.

reserved(R: 1 bit)—bit reserved for future use.

timestamp(32 bits)—denotes the timestamp field value present in thepacket header of the MMTP packet first transmitted in the related FECsource/repair packet block.

SS_start_seq_nr[i](8+8*SSM bits)—denotes the lower 8+8*SSM bits of theminimum value of packet_sequence_number of the packets where thepacket_id value in the source packet block protected with the FEC repairpacket is the same as the ith packet_id value provided in the AL-FECmessage (encoded FEC flow loop). i is 0, 1, . . . , N−1, and N is thenumber of assets belonging to the encoded FEC flow.

L[i](2 bits)—denotes the length of SPB_length[i] field positionedsubsequent. The length of SPB_length[i] field is, e.g., “6+8*L[i]”.

SPB_length[i](6+8*L[i] bits)—denotes(SS_end_seq_nr[i]−SS_start_seq_nr[i]+1) value. Here, SS_end_seq_nr[i]denotes the lower 8+8*SSM bits of the maximum value ofpacket_sequence_number of the packets where the packet_id value in thesource packet block protected with the FEC repair packet is the same asthe ith packet_id value provided in the AL-FEC message (encoded FEC flowloop).

When the value of the D field is, e.g., “0,” the value of the fielddenotes the number of the packets where the packet_id value in thesource packet block protected with the FEC repair packet is the same asthe ith packet_id value provided in the AL-FEC message (encoded FEC flowloop).

L2(2 bits)—denotes the length of the RSB_length field located after. Thelength of the RSB_length field is, e.g., “6+8*L2” bits.

RSB_length(6+8*L2 bits)—denotes the number of repair symbolsconstituting the related repair symbol block.

L3(2 bits)—denotes the length of the LRSB_length field located after.The length of the LRSB_length field is, e.g., “6+8*L3” bits. The fieldexists only when the value of the F field is, e.g., “1.”

LRSB_length(6+8*L3 bits)—denotes the number of repair symbolsconstituting the associated length repair symbol block. The field existsonly when the value of the F field is, e.g., “1.” When this field doesnot exist although the value of the I field is “1,” this denotes thatthe number of length repair symbols constituting the repair symbol blockis the same as the number of repair symbols constituting the repairsymbol block associated with the FEC repair packet.

L4(2 bits)—denotes the length of the SSB_length field located after. Thelength of the SSB_length field is, e.g., “6+8*L4” bits. This fieldexists only when SSBG Mode 2 is used.

SSB_length(6+8*L4 bits)—denotes the number of source symbolsconstituting the associated source symbol block. This field exists onlywhen SSBG Mode 2 is used.

L5(2 bits)—denotes the length of the LRS_ID field located after. Thelength of the LRS_ID field is, e.g., “6+8*L5” bits. The field existsonly when the value of the N field is, e.g., “1.”

LRS_ID(6+8*L5 bits)—denotes an integer for identifying the first lengthrepair symbol included in the FEC repair packet. This starts from avalue, e.g., 0, given in the length repair symbol block, and increasesby one per repair symbol. The field exists only when the value of the Nfield is, e.g., “1.” When this field does not exist although the valueof the I field, this denotes that the value of the field is the same asthe value of the RS_ID field.

L6(2 bits)—denotes the length of the LSB_length field located after. Thelength of the LSB_length field is, e.g., “6+8*L6” bits. The field existsonly when the value of the F field is “1.”

LSB_length(6+8*L6 bits)—denotes the number of length symbolsconstituting the associated length symbol block. The field exists onlywhen the value of the F field is, e.g., “1.” When this field does notexist although the value of the I field is “1,” this denotes that thenumber of length symbols constituting the length symbol block is thesame as the number of source symbols constituting the source symbolblock associated with the FEC repair packet.

L7(2 bits)—denotes the length of the num_LRS field located after. Thelength of the num_LRS field is, e.g., “6+8*L7” bits. The field existsonly when the value of the N field is, e.g., “1.”

num_LRS(6+8*L7 bits)—denotes the number of length repair symbolsconstituting the length repair data of the FEC repair packet. The fieldexists only when the value of the N field is, e.g., “1.” When the fielddoes not exist although the value of the I field is “1,” this denotesthat the value of the field is identical to the number of repair symbolsincluded in the current FEC repair packet.

RS_ID(24 bits)—is a sequence number for identifying the first repairsymbol included in the corresponding FEC repair packet. When the FECrepair packet includes two or more repair symbols, the sequence numberof the repair symbols subsequent to the first repair symbol increases bya given value, e.g., 1. For all the repair symbol blocks, it starts witha given value, e.g., 0, and increases by a given value, e.g., 1, perrepair symbol. The field is transmitted in lower 24 bits of thepacket_sequence_number field of the MMTP packet header.

The above-described FEC payload ID mode 1 is for the FEC operation thatdoes not use the source FEC payload ID and transfers, to the receivingdevice, where each MMT packet (source packet) is positioned in thesource symbol block, using the repair FEC payload ID.

When the above-described SSBG Mode 2 is used, the position of the sourcepacket in the source symbol block may depend on the lengths of othersource packets previous to the source packet. The packet_sequence_numberfield value of the MMT packets (source packets) having the samepacket_id belonging to the source packet block may have a discontinuitydue to dropped packets. In this case, additional length repair data isrequired to reconfigure the source symbol block using the FEC sourcepacket received by the receiving device.

To that end, the transmitting device may generate the length repairsymbol block constituted of one or more length repair symbols protectingthe length symbol block. The length symbol block may consist of lengthsymbols, and each length symbol may have a constant size of two bytes.The constant value denotes the length of the MMTP packet belonging tothe “virtual source packet block.”

Let's say that among the packet_sequence_number's of the MMT packetshaving the same packet_id belonging to the source packet block, theminimum value is Smin (packet_id) and the maximum value is Smax(packet_id). At this time, the “virtual source packet block” includesthe MMT packet included in the associated source packet block and thedropped MMT packet which has the packet_id protected with the sourcepacket block and where the packet_sequence_number value is in the rangeof {Smin(packet_id)+1, Smin(packet_id)+2 . . . Smax(packet_id)−1}. Thedropped packet is not transmitted on an actual channel nor is itprotected by FEC. The value of the length symbol associated with thedropped packet may be set to a preset value (e.g., 0).

In the above-described embodiment, the length repair symbol is generatedthrough the same FEC code as the associated FEC repair flow. Accordingto an implementation, the length repair symbol may also be generatedusing an FEC code different from the FEC code. However, in this case,the other FEC code used should be provided to the receiving device. Thevalue of the remaining length symbol when the number of length symbolsconstituting the length symbol block is larger than the number of MMTpackets belonging to the “virtual source packet block” may be set to apredetermined value (e.g., 0).

Meanwhile, cases where num_LRS_flag field denotes whether the number oflength repair symbols included in the length repair data of the currentFEC repair packet is the same as the number of repair symbols includedin the current FEC repair packet have been described above.

However, it should be noted that the num_LRS_flag field may be used notonly in the above form but in the following form as well.

num_LRS_flag(N, 1 bits)—denotes whether the number of length repairsymbols included in the length repair data of the current FEC repairpacket has the same sequence number as repair symbols included in thecurrent FEC repair packet.

When the value is set to, e.g., “0,” the length repair data shouldinclude the same number of repair symbols as the number of repairsymbols included in the current FEC repair packet. The sequence numberof each length repair symbol should be the same as the sequence numberof the repair symbol in the same order. Further, the L5, LRS_ID, L7, andnum_LRS fields should be absent.

When the value is set to, e.g., “1,” the L5, LRS_ID, L7 and num_LRSfields should necessarily exist. This denotes that the number of lengthrepair symbols included in the length repair data of the current FECrepair packet and the sequence number of each length repair symbol aresignaled via the fields.

The field should be set to “0” when the value of I field is “0” and,when the value of the F field is “1,” it should be set to “1.”. Further,for the FEC repair packets belonging to one FEC repair packet block, thevalue of the field should be set to be identical.

This is described below again.

num_LRS_flag(N, 1 bits)—denotes whether the identifier values of thelength repair symbols included in the length repair data of the FECrepair packet are the same as the identifier values of the repairsymbols transferred by the corresponding FEC repair packet.

As an example, when the number of length repair symbols included in thelength repair data is the same as the number of repair symbols includedin the FEC repair packet, the value of the num_LRS_flag field may be setto “0.” In this case, the identifier of each length repair symbol mayhave the same value in the same order as the identifier of the repairsymbol. In this case, the repair FEC payload ID may lack the L5 field,LRS_ID field, L7 field, and num_LRS field.

As another example, when the repair FEC payload ID has the L5 field,LRS_ID field, L7 field, and num_LRS field, the value of the num_LRS_flagfield may be set to “1.” In this case, the number of length repairsymbols and the identifier value of the first length repair symbolincluded in the length repair data of the FEC repair packet may beexplicitly provided.

Further, when the value of the I field is set to, e.g., “0,” the valueof the num_LRS_flag field may be set to “0.” When the value of the Ffield is set to, e.g., “1,” the value of the num_LRS_flag field may beset to “1.” The value of the num_LRS_flag field would be the same forall the FEC repair packets included in the FEC repair packet block.

According to an embodiment, in the receiving device, the FEC decoder mayrepair the MMT packet length information using the length repair data,reconstruct the related source symbol block using the repaired lengthinformation, and perform FEC decoding, restoring the source symbol. Whenthe length of the repaired MMT packet is 0, it may be regarded as adropped packet.

It is hypothesized that a source symbol block including K source symbolsis generated from a source packet block including K′ MMT packets (sourcepackets) using the SSBG Mode and the source symbol block is protected bya repair symbol block including P repair symbols. At this time, therepair symbol may be generated using the same parameter as the parameterused to protect the source symbol block. This means that a length sourcesymbol is configured of K length symbols and that a length repair symbolblock is configured of P length repair symbols. At this time, the valueof the first K′ length symbols may be set to the MMT packet length ofthe relevant source packet block, and the value of the remaining K-K′length symbols may be set to 0.

Of course, the position of each field included in the repair FEC payloadID shown in FIG. 15 may be changed.

FIG. 16 is a view illustrating an example source symbol block generatedusing ssbg_mode 2 in a broadcast system according to an embodiment ofthe disclosure. FIG. 17 is a view illustrating an example length symbolblock for protecting packet length information in a broadcast systemaccording to an embodiment of the disclosure.

According to an embodiment, the transmitting device generates P lengthrepair symbols and transmits the length repair symbols as length repairdata of an FEC repair packet. In this case, the length repair symbol andthe repair symbol having the same identification value may be includedand transmitted in the same packet. In the above-described embodiment ofrepair FEC payload ID, the LRS_ID may be omitted.

It is hypothesized that in a virtual source packet block configured ofK′ MMP packets, p MMT packets are not transmitted, and a source packetblock configured of K′-p MMT packets is used. At this time, thepacket_sequence_number field value of the MMT packets having the samepacket_id belonging to the source packet block may have a discontinuitydue to dropped packets.

FIG. 18 is a view illustrating an example encoding symbol block when apacket drop is applied in a broadcast system according to an embodimentof the disclosure.

Referring to FIG. 18, it may be identified that two MMT packets in avirtual source packet block including 10 MMT packets are not transmittedand, thus, the source packet block includes only eight MMT packets.

FIG. 19 is a view illustrating an example length encoding symbol blockwhen a packet drop is applied in a broadcast system according to anembodiment of the disclosure.

Referring to FIG. 19, it may be identified that since the virtual sourcepacket block includes 10 MMT packets, the length symbol block is alsocomprised of 10 length symbols.

FIG. 20 is a view schematically illustrating an operation procedure of atransmitting device in a broadcast system according to an embodiment ofthe disclosure

Referring to FIG. 20, the transmitting device inputs a source packetblock in step 2010. In step 2020, the transmitting device generates oneor more source symbol blocks using the input source packet block. Instep 2030, the transmitting device performs FEC encoding on thegenerated source symbol blocks, generating one or more repair symbolblocks.

In step 2040, the transmitting device determines whether to need toinclude the source FEC payload ID in the FEC source packet.

When the source FEC payload ID is needed to be included in the FECsource packet, the transmitting device generates one or more source FECpayload IDs in step 2080.

Unless the source FEC payload ID is needed to be included in the FECsource packet, the transmitting device checks whether the value of thepacket sequence number discontinuity indicator (discontinuity inpacket_sequence_number) field needs to be set to 1 in operation 2050.

The packet transmitted by the transmitting device may include thesequence number corresponding to the relevant packet. The receivingdevice may re-sort the packets received with the sequence numbers. Atthis time, when there is a discontinuity in the sequence numbers, i.e.,unless the packet with a specific sequence number is received, thereceiving device needs to identify the cause of the failure in receptionof the packet. That is, the receiving device needs to be able toidentify whether the packet reception failure results from a loss duringtransmission or a transmission drop by the transmitting device.

The value of the packet sequence number discontinuity indicator fieldmay indicate, e.g., whether the packet sequence discontinuity resultsfrom a packet drop. In this case, the transmitting device may determinethat the value of the packet sequence number discontinuity indicatorfield is supposed to be set to ‘1.’

Unless the value of the packet sequence number discontinuity indicatorfield needs to be set to 1, the transmitting device checks whether SSBGMode 2 needs to be applied in step 2060.

When SSBG Mode 2 needs to be applied, or the value of the packetsequence number discontinuity indicator field needs to be set to 1, thetransmitting device generates length repair data in step 2070.

When the length repair data is generated or the source FEC payload IDneeds to be included in the FEC source packet, the transmitting devicegenerates one or more source FEC payload IDs in step 2080.

Of course, various modifications may be made to the above-describedembodiments of operations of the transmitting device in thecommunication signal. As an example, the steps described above inconnection with FIG. 20 may overlap or occur in parallel or in adifferent order or multiple times.

As set forth above, it should be noted that the information that may berequired for the determinations in steps 2040, 2050, and 2060 may begiven as a result of the computations in steps 2010, 2020, and 2030 orbe determined based on transmission policies per service of thetransmitting device or per FEC-encoded packet flow.

Meanwhile, it should be noted that, although not shown in FIG. 20, thetransmitting device may include the process of generating the repair FECpayload ID.

FIG. 21 is a view schematically illustrating an operation procedure of areceiving device in a broadcast system according to an embodiment of thedisclosure.

Referring to FIG. 21, the receiving device detects a start of an MMTPsession in step 2210 and, in step 2120, receives an AL-FEC message fromthe transmitting device. The AL-FEC message may include packet_ids,ssgb_mode, fec_payload_id_mode. Described above in detail, the AM-FECmessage is not described below in further detail.

In step 2130, the receiving device may obtain the FEC source packet andFEC repair packet based on the received AL-FEC message. The receivingdevice checks whether the obtained FEC repair packet includes the sourceFEC payload ID in step 2140. When the result of checks reveals that thesource FEC payload ID exists, the receiving device performs AL-FECdecoding to repair the missing MMT packet in step 2180.

Unless the source FEC payload ID exists, the receiving device may, instep 2150, check whether the value of the Discontinuity inpacket_sequence_number field is set to 1 from the repair FEC payload IDof the FEC repair packet. When the result of checking shows that thevalue of the Discontinuity in packet_sequence_number field is set to 1,the receiving device may, in step 2170, perform AL-FEC decoding,restoring the length repair data. In step 2180, the receiving devicerepairs missing MMT packets by performing AL-FEC decoding.

Unless the value of the Discontinuity in packet_sequence_number field isset to 1, the receiving device checks whether SSBG Mode 2 has beenapplied in step 2160. If SSBG Mode 2 has not been applied, the receivingdevice, in step 2180, repairs missing MMT packets by performing AL-FECdecoding.

If SSBG Mode 2 has been applied, the receiving device, in step 2170,repairs the length repair data by performing AL-FEC decoding in step2170 and, in step 2180, performs AL-FEC decoding to thereby repairmissing MMT packets.

Although FIG. 21 illustrates the operation procedure by the receivingdevice in the broadcast system according to an embodiment of thedisclosure, various modifications may be made to FIG. 21. As an example,although the continuous steps are shown in FIG. 21, the steps of FIG. 21may overlap or arise in parallel or in different order, or severalnumber of times.

In the above-described embodiment of Repair FEC payload ID, the receiveris directly signaled whether there is a discontinuity in thepacket_sequence_number of the MMT packets with the same packet_id usingthe D field. Rather than directly signaling the discontinuity in thepacket_sequence_number, the receiving device may repair the length ofthe packets using the length repair data and then determine that aspecific value (e.g., 0) indicates a failure in transmission of packets.

FIG. 22 is a view schematically illustrating an internal structure of atransmitting device in a broadcast system according to an embodiment ofthe disclosure.

Referring to FIG. 22, the transmitting device 2200 includes atransmitter 2211, a processor 2213, a receiver 2215, and a storage unit2217.

First, the processor 2213 controls the overall operation of thetransmitting device 2200, in particular, operations related totransmission/reception of signals in a broadcast system. Operationsrelated to transmission/reception of signals in a broadcast system arethe same as those described above in connection with FIGS. 1 to 21, andno detailed description thereof is given below.

The transmitter 2211 transmits various signals and various messages toother devices included in a broadcast system under the control of theprocessor 2213. Various signals and messages transmitted by thetransmitter 2211 are the same as those described above in connectionwith FIGS. 1 to 21, and no detailed description thereof is repeated.

The receiver 2215 receives various signals and various messages fromother devices included in a broadcast system under the control of theprocessor 2213. Various signals and messages received by the receiver2215 are the same as those described above in connection with FIGS. 1 to21, and no detailed description thereof is repeated.

The storage unit 2217 stores a program and various data related tosignal transmission/reception performed by the transmitting device 2200under the control of the processor 2213.

The storage unit 2217 stores various signals and messages received bythe receiver 2215 from other devices.

FIG. 22 illustrates an example in which the transmitting device 2200 isimplemented with separate units, such as the transmitter 2211, theprocessor 2213, the receiver 2215, and the storage unit 2217. However,the transmitting device 2200 may be implemented as a combination of atleast two of the transmitter 2211, the processor 2213, the receiver2215, and the storage unit 2217.

Further, the processor 2213 of the transmitting device 2200 may beimplemented as at least one processor.

FIG. 23 is a view schematically illustrating an internal structure of areceiving device in a broadcast system according to an embodiment of thedisclosure.

Referring to FIG. 23, the receiving device 2300 includes a transmitter2311, a processor 2313, a receiver 2315, and a storage unit 2317.

The processor 2313 controls the overall operation of the receivingdevice 2300, in particular, operations related to transmission/receptionof signals in a broadcast system. Operations related totransmission/reception of signals in a broadcast system are the same asthose described above in connection with FIGS. 1 to 21, and no detaileddescription thereof is given below.

The transmitter 2311 transmits various signals and various messages toother devices included in a broadcast system under the control of theprocessor 2313. Various signals and messages transmitted by thetransmitter 2311 are the same as those described above in connectionwith FIGS. 1 to 21, and no detailed description thereof is repeated.

The receiver 2315 receives various signals and various messages fromother devices included in a broadcast system under the control of theprocessor 2313. Various signals and messages received by the receiver2315 are the same as those described above in connection with FIGS. 1 to21, and no detailed description thereof is repeated.

The storage unit 2317 stores a program and various data related tosignal transmission/reception performed by the receiving device 2300under the control of the processor 2313. The storage unit 2317 storesvarious signals and messages received by the receiver 2315 from otherdevices.

FIG. 23 illustrates an example in which the receiving device 2300 isimplemented with separate units, such as the transmitter 2311, theprocessor 2313, the receiver 2315, and the storage unit 2317. However,the receiving device 2300 may be implemented as a combination of atleast two of the transmitter 2311, the processor 2313, the receiver2315, and the storage unit 2317.

Further, the processor 2313 of the receiving device 2300 may beimplemented as at least one processor.

Particular aspects of the present invention may be implemented incomputer-readable codes on a computer-readable recording medium. Thecomputer readable recording medium is a data storage device that maystore data readable by a computer system. Examples of the computerreadable recording medium may include read only memories (ROMs), randomaccess memories (RAMs), compact disk-read only memories (CD-ROMs),magnetic tapes, floppy disks, optical data storage devices, and carrierwaves (such as data transmission over the Internet). The computerreadable recording medium may be distributed by computer systems over anetwork, and accordingly, the computer readable codes may be stored andexecuted in a distributed manner. Functional programs, codes, and codesegments to attain the present invention may be readily interpreted byskilled programmers in the art to which the present invention pertains.

The apparatuses and methods according to embodiments of the presentinvention may be implemented in hardware, software, or a combination ofhardware and software. Such software may be stored in a volatile ornon-volatile storage device such as a read-only memory (ROM) or otherstorage devices, a memory, such as a random access memory (RAM), amemory chip, a device or an integrated circuit, or a storage medium,such as, e.g., a compact disc (CD), a digital video disc (DVD), amagnetic disk, or a magnetic tape, which allows for optical or magneticrecording while simultaneously read out by a machine (e.g., a computer).The methods according to embodiments of the present invention may beimplemented by a computer or a portable terminal including at least oneprocessor and a memory, and the memory may be an exemplarymachine-readable storage medium that may properly retain program(s)containing instructions for implementing the embodiments of the presentinvention.

Accordingly, the present disclosure encompasses a program containingcodes for implementing the device or method set forth in the claims ofthis disclosure and a machine (e.g., computer)-readable storage mediumstoring the program. The program may be electronically transferred viaany media such as communication signals transmitted through a wired orwireless connection and the present disclosure properly includes theequivalents thereof.

The apparatuses according to embodiments of the present invention mayreceive the program from a program providing device wiredly orwirelessly connected thereto and store the same. The program providingapparatus may include a memory for storing a program includinginstructions enabling a program processing apparatus to perform a presetcontent protection method and information necessary for the contentprotection method, a communication unit for performing wired or wirelesscommunications with a graphic processing apparatus, and at least oneprocessor transmitting the program to the transmitting/receiving deviceautomatically or as requested by the graphic processing apparatus.

Although specific embodiments of the present disclosure have beendescribed above, various changes may be made thereto without departingfrom the scope of the present disclosure. Thus, the scope of the presentinvention should not be limited to the above-described embodiments, andshould rather be defined by the following claims and equivalentsthereof.

1. A method of generating a transmission packet by a transmitting devicein a broadcast system, the method comprising: generating a source symbolblock having plurality of source symbols using a source packet blockhaving a plurality of source packets by one generation mode of aplurality of generation modes (ssbg_mode #0, #1, #2); generating arepair symbol block for the generated source symbol block by one forwarderror correction (FEC) scheme of a plurality of forward FEC schemes (FECpayload ID mode 0, FEC payload ID mode 1); generating a source packet bythe plurality of source packets; and generating a repair packet by thegenerated repair symbol block, wherein generating the repair packetincludes: generating the repair packet in which length repair data and arepair FEC payload identifier (ID) are included in response to anoccurrence of a discontinuity of a packet sequence number, and a firstFEC scheme (FEC payload ID mode 1) being applied to generate the repairsymbol block.
 2. The method of claim 1, wherein a first flag (D:discontinuity flag) value of the repair FEC payload ID is configured toindicate the occurrence of the discontinuity of the packet sequencenumber in response to the occurrence of the discontinuity of the packetsequence number, and wherein in response to a specific flag value of therepair FEC payload ID being configured to indicate the occurrence of thediscontinuity of the packet sequence number, a second flag (I) value ofthe repair FEC payload ID is configured to indicate that the lengthrepair data is included in the repair packet.
 3. The method of claim 2,wherein a third flag (F: FEC_parameter_flag) value of the repair FECpayload ID is configured to indicate whether a same FEC code has beenused to generate the length repair data and generate the repair symbolblock considering the first flag (D) value and the second flag (I)value.
 4. The method of claim 3, wherein a fourth flag (N: num_LRS_flag)of the repair FEC payload ID is configured to indicate whether a numberof repair symbols included in the length repair data is the same as thenumber of repair symbols included in the repair packet considering thesecond flag (I) value and the third flag (F) value.
 5. The method ofclaim 1, wherein generating the repair packet further includesgenerating the repair packet to include the repair FEC payload ID andthe length repair data in response to the first FEC scheme (FEC payloadID mode 1) being applied to generate the repair symbol block and asecond generation mode (ssbg_mode #2) being applied to generate thesource symbol block, and wherein in response to the second generationmode (ssbg_mode #2) being applied to generate the source symbol block, asecond flag (I) value of the repair FEC payload ID is configured toindicate that the length repair data is included in the repair packet.6. The method of claim 5, wherein a third flag (F: FEC_parameter_flag)value of the repair FEC payload ID is configured to indicate whether asame FEC code has been used to generate the length repair data andgenerate the repair symbol block considering the second flag (I) value.7. The method of claim 6, wherein a fourth flag (N: num_LRS_flag) of therepair FEC payload ID is configured to indicate whether a number ofrepair symbols included in the length repair data is the same as thenumber of repair symbols included in the repair packet considering thesecond flag (I) value and the third flag (F) value.
 8. The method ofclaim 4, wherein the repair FEC payload ID further includes informationabout a length configured considering the first to fourth flags.
 9. Atransmitting device of a broadcast system, comprising: a transmitterconfigured to transmit a transmission packet to an external device for abroadcast service; and at least one processor connected with thetransmitter and configured to generate the transmission packet for thebroadcast service, wherein the at least one processor is configured to:generate a source symbol block having plurality of source symbols usinga source packet block having a plurality of source packets by onegeneration mode of a plurality of generation modes (ssbg_mode #0, #1,#2), generate a repair symbol block for the generated source symbolblock by one forward error correction (FEC) scheme of a plurality offorward FEC schemes (FEC payload ID mode 0, FEC payload ID mode 1),generate a source packet by the plurality of source packets, andgenerate the repair packet in which length repair data and a repair FECpayload identifier (ID) are included in response to an occurrence of adiscontinuity of a packet sequence number, and a first FEC scheme (FECpayload ID mode 1) being applied to generate the repair symbol block.10. The transmitting device of claim 9, wherein the at least oneprocessor is configured to: configure a first flag (D: discontinuityflag) value of the repair FEC payload ID to indicate the occurrence ofthe discontinuity of the packet sequence number in response to theoccurrence of the discontinuity of the packet sequence number, and inresponse to a specific flag value of the repair FEC payload ID beingconfigured to indicate the occurrence of the discontinuity of the packetsequence number, configure a second flag (I) value of the repair FECpayload ID to indicate that the length repair data is included in therepair packet.
 11. The transmitting device of claim 10, wherein the atleast one processor is configured to configure a third flag (F:FEC_parameter_flag) value of the repair FEC payload ID to indicatewhether a same FEC code has been used to generate the length repair dataand generate the repair symbol block considering the first flag (D)value and the second flag (I) value.
 12. The transmitting device ofclaim 11, wherein the at least one processor is configured to configurea fourth flag (N: num_LRS_flag) of the repair FEC payload ID to indicatewhether a number of repair symbols included in the length repair data isthe same as the number of repair symbols included in the repair packetconsidering the second flag (I) value and the third flag (F) value. 13.The transmitting device of claim 9, wherein the at least one processoris configured to: generate the repair packet to include the repair FECpayload ID and the length repair data in response to the first FECscheme (FEC payload ID mode 1) being applied to generate the repairsymbol block and a second generation mode (ssbg_mode #2) being appliedto generate the source symbol block; and in response to the secondgeneration mode (ssbg_mode #2) being applied to generate the sourcesymbol block, configure a second flag (I) value of the repair FECpayload ID to indicate that the length repair data is included in therepair packet.
 14. The transmitting device of claim 13, wherein the atleast one processor is configured to configure a third flag (F:FEC_parameter_flag) value of the repair FEC payload ID to indicatewhether a same FEC code has been used to generate the length repair dataand generate the repair symbol block considering the second flag (I)value.
 15. The transmitting device of claim 14, wherein the at least oneprocessor is configured to configure a fourth flag (N: num_LRS_flag) ofthe repair FEC payload ID to indicate whether a number of repair symbolsincluded in the length repair data is the same as the number of repairsymbols included in the repair packet considering the second flag (I)value and the third flag (F) value.
 16. The transmitting device of claim12, wherein the repair FEC payload ID further includes information abouta length configured considering the first to fourth flags.
 17. A methodof restoring a transmission packet by a receiving device in a broadcastsystem, the method comprising: receiving a source packet including aplurality of source packets and a repair packet including a repairsymbol block; identifying whether a packet sequence number isdisconnected and a fist FEC scheme (FEC payload ID mode 1) among aplurality of FEC schemes (FEC payload ID mode 0, FEC payload ID mode 1)is applied, to generate the repair symbol block based on a plurality offlags included in a repair forward error correction (FEC) payloadidentifier (ID) of the repair packet; decoding length repair data of therepair packet in response to an occurrence of the packet sequence numberand the first FEC scheme (FEC payload ID mode 1) being applied; andrestoring a missing transmission packet using the decoded length repairdata, wherein the plurality of flags include a first flag (D:discontinuity flag) indicating that the discontinuity of the packetsequence number has occurred, a second flag (I) indicating whether thelength repair data is included in the repair packet, a third flag (F:FEC_parameter_flag) indicating whether the same FEC code is used togenerate the repair symbol block and the length repair data, and afourth flag (N: num_LRS_flag) indicating whether a number of repairsymbols included in the length repair data is the same as the number ofrepair symbols included in the repair packet, and wherein the repair FECpayload identifier (ID) further includes information about a lengthconfigured considering the first to fourth flags.
 18. The method ofclaim 17, further comprising: identifying whether a second generationmode (ssbg_mode #2) for the source packet has been applied among aplurality of generation modes (ssbg_mode #0, #1, #2) generating a sourcesymbol block using a source packet block, and the first FEC scheme (FECpayload ID mode 1) is applied to generate the repair symbol block; anddecoding the length repair data of the repair packet in response to thefirst FEC scheme (FEC payload ID mode 1) and the second generation mode(ssbg_mode #2) having been applied.
 19. A receiving device of abroadcast system, comprising: a receiver configured to receive a sourcepacket including a plurality of source packets and a repair packetincluding a repair symbol block; and at least one processor connectedwith the receiver and configured to repair a source packet receivedthrough the receiver, wherein the at least one processor is configuredto: identify whether a packet sequence number is disconnected and a fistFEC scheme (FEC payload ID mode 1) among a plurality of FEC schemes (FECpayload ID mode 0, FEC payload ID mode 1) is applied, to generate therepair symbol block based on a plurality of flags included in a repairforward error correction (FEC) payload identifier (ID) of the repairpacket, decode length repair data of the repair packet in response to anoccurrence of the packet sequence number and the first FEC scheme (FECpayload ID mode 1) being applied, and repair a missing transmissionpacket using the decoded length repair data, wherein the plurality offlags include a first flag (D: discontinuity flag) indicating that thediscontinuity of the packet sequence number has occurred, a second flag(I) indicating whether the length repair data is included in the repairpacket, a third flag (F: FEC_parameter_flag) indicating whether the sameFEC code is used to generate the repair symbol block and the lengthrepair data, and a fourth flag (N: num_LRS_flag) indicating whether anumber of repair symbols included in the length repair data is the sameas the number of repair symbols included in the repair packet, andwherein the repair FEC payload identifier (ID) further includesinformation about a length configured considering the first to fourthflags.
 20. The receiving device of claim 19, wherein the at least oneprocessor is configured to: identify whether a second generation mode(ssbg_mode #2) for the source packet has been applied among a pluralityof generation modes (ssbg_mode #0, #1, #2) generating a source symbolblock using a source packet block, and the first FEC scheme (FEC payloadID mode 1) is applied to generate the repair symbol block, and decodethe length repair data of the repair packet in response to the first FECscheme (FEC payload ID mode 1) and the second generation mode (ssbg_mode#2) having been applied.